An image forming apparatus of a particular type known in the art includes a drum supporting member configured to support a plurality of photoconductor drums and removably installed in a casing of the apparatus, a scanner configured to emit a laser beam directed to the plurality of photoconductor drums to expose each photoconductor drum to the laser beam, and a sheet output tray portion configured to receive a sheet being ejected with an image formed thereon by the plurality of photoconductor drums and other components of the apparatus. To be more specific, the sheet output tray portion in this type of the image forming apparatus is configured to include a first wall and a second wall wherein the first wall extends from an upper wall of the casing of the apparatus in a downward direction perpendicular to the upper wall, and the second wall extends obliquely upward, gently curing so as to upwardly bulge like an arc as viewed in cross section, from a lower end of the first wall toward the upper wall of the casing of the apparatus. The first wall has an ejection port formed therein for a sheet to be ejected therethrough.
Also in this type of the image forming apparatus, a scanner is disposed in a space under the upwardly bulging second wall (i.e., under the sheet output tray portion), and the drum supporting member is disposed below the bottom of the sheet output tray portion (i.e., below the lower end of the first wall).